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v3.20.4

Credit Facilities, Long-Term Debt and Lease Liabilities - Debentures (Details) - CAD ($) $ in Millions | Nov. 25, 2020 | Aug. 02, 2018 | Dec. 31, 2020 | Oct. 22, 2020 | Dec. 31, 2019 | Jul. 20, 2018
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Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |
Interest rate |  |  |  | 4.07% |  | 4.509%
Borrowings |  |  | $ 3,361 |  | $ 3,212 |
Debentures |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |
Interest rate |  | 6.40% |  |  |  | 6.40%
Borrowings |  | $ 400 | $ 249 |  | $ 647 |
Redemption of noncurrent borrowings |  | 425 |  |  |  |
Redemption of prepayment premium recognized in net interest expense |  | 19 |  |  |  |
Accrued and unpaid interest |  | $ 6 |  |  |  |
Debentures | Minimum |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |
Interest rate |  |  | 6.90% |  |  |
Debentures | Maximum |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |
Interest rate |  |  | 7.30% |  |  |
Medium Term Notes |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |
Interest rate | 5.00% |  |  |  |  |
Borrowings, Redemption | $ 400 |  |  |  |  |

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